BearOfNH

Feb 5th, 1962 is often a good test date. Sun, Mercury, Venus, Earth, Jupiter lined up at the same time as a total solar eclipse. Mars and Saturn weren't too far away (15°) either. Many in the woo-woo community consider this day to be the start of the Age of Aquarius, for whatever that's worth.

Thanks for the pointer, 00007. The article is well-written and concise. The thrust of the article is that when the solar system crosses the plane of the galaxy (every 30-35 million years), gravitational effects increase enough to where there's a lot more Oort cloud perturbations possible, and this can lead to a storm of comets heading into the inner solar system. (An "Oort storm"?) But I wasn't asking about the Oort cloud specifically. That's just an example I called upon to show where the term "passing stars" was used. Maybe I could have phrased it better, but I really wanted to know more about "passing stars". There seems to be little in the way of hard evidence these things exist. One can make statistical arguments, but there seems to be little in the way of observational evidence. And therefore it seems somewhat disingenuous for astronomers to pull "passing star" out of a hat when, for all we know, there hasn't been even one since the formation of the solar system.

On American cable and satellite TV there are a number of astronomy / cosmology programs speaking to the creation of our solar system, and various means of our eventual destruction. One method of destruction involves disturbing the Oort cloud, freeing a comet to fall in to the inner solar system and >BLAM< smash into the earth. If Jupiter doesn't catch it first, etc. OK, but how does the Oort cloud get so disturbed in the first place? This is where it gets annoying. One standard excuse on these TV shows is that a "passing star" disturbs the otherwise peaceful comet cloud. What exactly is a "passing star"? I'm going to assume it's a star that passes by the solar system within, say, 4.3 ly distance. I doubt anything farther out than AC will affect the Oort cloud. (Or if it does, we're probably all doomed and these definitions won't matter anyway). I took astronomy in college (over 40 years ago) but never heard of "passing stars" in that course. I can see how a "passing star" might show up now and then as the solar system winds its way across a galactic arm. But intuitively that doesn't seem too frequent an event. Is there any other way to disturb the Oort cloud? If they're real, how frequent are these passing stars? Astronomers discover things and announce and catalog them all the time. But I have never heard announcements of any passing stars being discovered. Has anybody actually found a passing star in our lifetimes? Is there a catalog of such stars? Is anybody specifically looking for them? I guess this is what bothers me. Scientists of high repute (e.g., Michio Kaku, Alexei Filippenko) call upon things that may never happen to illustrate ... ... wait for it ... ... how something might happen.

From the link: So somewhere off in the distant future there will be a big bang inside "our" universe, eventually expanding and wiping out our universe. Hmmm...doesn't that mean our universe is probably doing the same thing to a "parent" universe, too?

I read it (D=2,500,000) as 2.5 million meters or 1550 miles. Yes, still a major expenditure. Fixing / correcting for meteorite impacts would present an interesting technical challenge.

I was thinking more of the case of an uncivilized panet. Or at least, a planet without cities. You might pick the North pole and the top of the highest mountain and draw the PM thru those points, but that runs the risk of changing geologically. If the planet is already inhabited and civilized, they probably also have their own PM.

One tricky problem is determining the Prime Meridian, i.e., the line representing 0° longitude. It's arbitrary, but how do you decide?